Tracking the implementation state of an RFC

[brianraymor]

The current RFC proposal states:

NOTE: The existence of an approved software RFC does not indicate any particular priority or commitment to implement the RFC, nor is an approved RFC a green light to implement. Approved RFCs simply demonstrate community agreement on a technical decision. Product priorities are managed and implementations scheduled via the DCP PM planning process.

As a result, there's no indication whether the RFC was actually implemented.

The Rust template includes a Rust issue # for tracking the state of a related implementation.

It's also possible to recommend that subsequent DCP implementation issues reference the RFC and change its label to "rfc-implemented".

In any case, this needs additional thought.